Gas turbine engines conventionally comprise an axial flow compressor which compresses air to the proper density required for supporting combustion of fuel in a combustion chamber. The combustion gases then pass to a turbine which powers the axial flow compressor. After passing through the turbine, the combustion gases may be employed to drive a power turbine which is connected to an output shaft on which may be mounted a propeller, generator or other device such as for marine or industrial purposes.
The combustion of fuel within the combustion chamber results in intensely heated combustion gases which heat the walls of the combustion chamber and the various turbine components as the gases pass through the turbine. Increasing combustion firing temperatures can improve shaft horsepower, specific fuel consumption and efficiency of the engine. However, the ability to increase these temperatures is limited by the ability of the engine components such as the combustion chamber and the turbine to withstand increased temperatures. Therefore, to avoid overheating, cooling methods have been developed to cool combustors, and turbine vanes and blades.
Conventional cooling techniques provide that some of the air input into the engine through the compressor is diverted and used as a coolant. Typically, the diverted air passes outside the combustion chamber and enters passageways which flow around the combustion chamber and then through cooling passages in the turbine blades.
Other cooling techniques have included the use of steam in which steam is introduced into the interior of the blading and exits tangentially onto the exterior surfaces of the blading such as to thermally insulate the blades from the hot combustion gases. This technique has some advantages since the specific heat of steam is much greater than air and therefore steam is a much better coolant. However, the steam used in cooling reduces overall system performance since this steam bypasses some of the the engine's flowpath turbine stages and, therefore, is not injected in the engine as described by my U.S. Pat. No. 4,631,914 entitled "Gas Turbine Engine of Improved Thermal Efficiency," issued Dec. 30, 1986, and by K. O. Johnson in U.S. Pat. No. 4,569,195 entitled "Fluid Injection Gas Turbine Engine And Method for Operating" issued Feb. 11, 1986. Therefore, it would be desirable to have an improved method of engine cooling which does not significantly inhibit system performance.